Vatapi was the younger brother of the Daitya Ilvala, the ruler of the city of Manimati. He was a shape-shifter. His brother was denied a boon by the sage Agastya, and hence the brothers became the enemies of Brahmanas.

When any Brahmana guest arrived at the palace, Vatapi would transform into a ram. Ilvala would then cause the meat of this ram to be served to the unsuspecting guest. Once the Brahmana had eaten his fill, Ilvala would utter a magical incantation, and say, "O Vatapi, come out!". Vatapi would then emerge whole and alive from the belly of the guest, killing that Brahmana in that process.